Several patents have issued in U.S.Class 277-178 directed to the problem of seal wear owing to abrasion occasioned by repeated flexing. However, some of the seals lack sufficient flexibility, some are very complex to manufacture and too costly, while others do not maintain a tight seal over a sufficiently wide range of temperatures and other conditions encountered in use. As a matter of fact, prior art seals experience some leakage at one or the other of the temperature extremes normally encountered, and it is an important purpose of the present invention to overcome this type of leakage while providing a simple, easy to use, and long-lived seal.